Synchronism correction for multiplex



A ril 21, 1936.

R. E. MATHES 2,038,375

SYNCHRONISM CORRECTION FOR MULTIPLEX Filed Dec. 1, 1952 2 Sheets-Sheet 2 i' '5 3a, 39 E o I I I I V I we 2a '5 g- '37 i 1 g i E 36 g INVENTOR- R.E.MATHE5 ATTORN EY- Patented Apr. 21, 1936 PATENT OFFICE SYNCHRONISM CORRECTION FOR MULTIPLEX Richard E. Mathes, Westfield, N.

Radio Corporation of Delaware J assignor to America, a corporation of Application December 1, 1932, Serial No. 645,171

12 Claims.

This invention is concerned with the correction of speed'and phase synchronism of rotating machinery in communication systems, and is particularly applicable to such of these systems which require no special pulse or signal to be sent for correction purposes.

In the transmission of intelligence by facsimile and multiplex telegraph systems operating on the time division principle, it becomes necessary to maintain quite close synchronism between the transmitting and receiving stations. Hitherto, the usual practice has been to provide local standard speed or frequency controls at each station, and to correct the phase and synchronism at the receiver in accordance with either the transmitted intelligence bearing signal elements or else by means of a special correction signal transmitted periodically at short intervals.

The use of a special signal for this purpose has diminution of the time available for the intelligence bearing signals and so reduces the speed of the system to that extent. An economic use of suchmethod of phase and'synchronism control would require that not more than, say, 5% of the circuit time be assigned to the special correction signal, a requirement which necessitates the transmission of special signals-at rare intervals, thus making it imperative to have a large amount of tolerance in the length and spacing of the intelligence bearing signal elements themselves to provide for possible phase displacement between the transmitter and receiver during the time between corrections. Consequently, there results a still further reduction in the effective intelligence speed.

As for deriving the correction or phasing directly from the transmitted signal elements themselves in accordance with prior methods, experience has shown that it is impossible to transmit telegraph signals without distortion, the amount and type of which, depends upon the transmission circuit. For example, on a radio circuit fortuitous distortion may be especially bothersome. This type of distortion causes either over or under correction, and thus requires comparatively large tolerance limits in the signal lengths to absorb the resultant floating. I

The foregoing difficulties are overcome in accordance with the present invention by the provision of an auxiliary circuit in the receiver which, together with a distributor segment or cam arrangement, produces pulses whose times of occurrence are utilized to affect a speed con- 5 trolling device. More specifically, the auxiliary been found to be undesirable since it results in a (o1. int-69.5) I

circuit is arranged to pass pulses upon the start and stop of each signal element, the occurrence of one of which, whose polarity is of the desired type, is compared from a point oi time standpoint with the close of a circuit by the cam arrangement, thus enabling an indication as to the amount the receiver is out of phase with respect to the transmitter. The cam is sopositioned that the production of a pulse and the closure of the circuit occur simultaneously only when the receiver and transmitter are in absolute phase. The time interval between the production of the pulse and the closure of the circuit is integrated by a circuit, in a manner to behereinafter described, to control the speed of the rotating machinery at the receiver. In actual practice, the time intervals of successive signal elements are compared so as to obtain an average value, which average should extend over several successive time intervals in order to compensate for fortuitous distortion. Preferably, this should be a running average so that it may be applied for correction more often than the average of a discrete group of successive time intervals. This average is then used to operate the correction mechanism an amount depending upon its alue.

One advantage of the present invention lies in the mode of connecting the phase and synchronizing apparatus to the telegraph receiving apparatus in such manner as not to disturb the signal envelope as it is subsequently available for receiving purposes. This is effected by means of a coupling tube.

In the accompanying drawings, Figure 1 shows, diagrammatically, a system for accomplishing correction in accordance with the present invention; and Figure 2 shows an alternative and improved system for maintaining synchronism and phase. Figures 1a and 2a show, in cross section, views of different cam arrangements employed in Figures 1 and 2 respectively.

Referring to Figure 1, there is shown, in conventional box form, a transmitter station I which is arranged to transmit signals over any suitable type of communication circuit 2, such as a landline or radio channel, to a receiving station comprising suitable terminal receiving apparatus 3,

, a rectifier 4, and additional equipment for phase and correction purposes which will be described in more detail later.

The incoming signal, which, for the purpose of this description, will be assumed to be a tone, is fed via a transformer 5 to the rectifier shown diagrammatically in box 4. Signal current passing through rectifier 4 causes an IR drop across resistance I which effectively produces varying potentials on the grid of a coupling vacuum tube 8..

in the plate circuit of which are the primaries of two transformers 9 and III. If desired, a low pass filter II may be inserted between rectifier 4 and resistance 7 for smoothing out whatever tone components remain in the rectified signal. Since telegraphic signals generally approximate the form of a square wave, a pulse current will be generated by the transformers 9 and II in the secondaries thereof during the transition period from space to mark and vice versa. No current, however, will be generated in the secondaries of these transformers during the intervals of steady space or mark. This generated impulse in transformer 9 is applied between the grid and cathode of a grid glow discharge relay tube II, and, if of the proper polarity, will cause the grid glow tube II to strike and pass'plate current to the circuit including resistance II, the anode and cathode of the tube and the parallel resistance and capacity circuit I 3, I4 to negative potential, provided the circuit is closed through the wiper springs I5 of cam I6. This circuit will then pass current so long as these wiper springs remain closed by means of one of the steel pins II, but will cease to pass current upon the opening of the springs. Condenser I4 has a large capacity of the order of some four microfarads, or so, and resistance I3 is also designed large, of the order of, say, one megohm so as to cause the condenser I 4 to be comparatively rapidly charged as the current passes through the grid glow tube I I. In this manner there is placed a corresponding potential upon the grid of vacuum tube I9 effectively permitting it to pass current to actuate relay I9.

Wiper springs I5 are arranged to be closed momentarily at predetermined intervals through the operation of a drum or disc of insulating material I 6 which is rotated by the motor to be controlled 29 and which carries steel pins I! mounted on and projecting from its periphery. The placement of pins I1 and the speed of rotation of the cam or disc I8 are so chosen as to cause a momentary closure of the circuit through the wiper springs I5 once for each dot length of the incoming telegraph signals. Furthermore, this closure is designed to be only some 5% to 10% of the duration of such dot length.

The motor 20 which it is intended to control is preferably so arranged that its stator casting and stator winding, normally fixed or stationary, may be rotated about the axis of the rotor. The rotation of this stator casting (which is usually the motor field frame) is effective through the operation of a small correction motor II which is responsive to the functioning of contact 22 of relay I 9, an obvious circuit for which is shown in the drawings.

Assuming that the disc or cam arrangement I 6 ca y ng steel pins I1, which will hereinafter be called the kicker, is rotating, and, further, that the pulses to strike the grid glow tube II occur only upon the transition period from space to mark or vice versa, it will be evident that when the motor 20 is running at such speed and phase that the wiper contacts I5 close just at or just before the occurrence of the pulse in transformer 9, the grid glow tube II will then pass a pulse of current on to the circuit I3, I l, the length of which will be determined by the length of closure of the wiper springs I5. Due to the resistance and capacity constants of the circuits chosen there will occur only a partial charge on condenser I4 and. if the same cycle of operations occurs at the next dot mark, another partial charge will be placed on condenser It in addition to that already obtained. This action will repeat until the charge on condenser I4 is suiliciently large to cause the grid of tube l9 to reach a polarity such as to permit the plate current of tube I8 to actuate relay I9. Closure of the relay contacts 22 will close an obvious circuit through a volt D. C. source to the correction motor 2| to cause it to rotate the field casting of the control motor 29 and, inasmuch as the latter is maintaining a certain fixed synchronism and phase between its armature and any given point on the casting, the result will be a slight change in the phase position of steel pins II carried by the kicker IS, with respect to the stationary brushes.

This change or advancement in the position of the pins will cause the complete closure of the wiper springs l5 to occur ahead of the pulse from the transformer 9; consequently, glow tube I I will then not pass current upon the successive closures and successive pulses. Condenser It will then slowly discharge through resistance I3 until the tube I9 blocks and releases relay I9, thus opening contacts 22 and stopping the rotation of correction motor 2|. As the controlled motor 20, which is arranged to be driven somewhat slower than the true synchronous speed, slowly loses phase with the incoming telegraphic signals, the closure of the wiper springs will more and more closely approach the time of occurrence of the pulse in transformer 9 until finally the grid glow tube II is caused to strike upon the occurrence of the pulses, and will again repeat the cycle of operations which slowly charges condenser I 4.

From the foregoing, it will be apparent that the motor to be controlled is corrected at intervals, depending upon the diiierence between the speed of its driving source and the speed of the incoming telegraphic intelligence bearing signals. This has been accomplished by using the transition periods in the telegraphic signal from space to mark to actuate the correcting mechanism,

thus eliminating the necessity for providing special correction signals which cause loss in circuit time. It is to be noted that because of the short time of closure of the wiper springs I5 it is impossible for most static and interference pulses to enter the correction system and cause false charges to be placed upon the condenser I4 with the resultant false correction of the motor 2|. Furthermore, due to the fact that all telegraphic signals have a certain amount of fortuitous distortion inherent in them which is random and,

therefore, occurs at no fixed interval or period of time, the requirement of having several pulses to charge the condenser I4 to a valve sufficient to make the correction circuit operative provides an averaging action and, consequently, protection against errors in correction arising from undesired causes.

In order to indicate when the motor 20 is in synchronism and, further, how much phase hunting is present, there is provided a neon lamp 23 in circuit with the secondary winding of transformer II], the light of which strikes in accordance with the incoming signals and is directed upon the "kicker disc so that the steel pins I! will reflect this light when they are in proper phase with the pulses originating from the incoming signals.

Figure 2 shows an alternative and improved method of maintaining synchronism and phase. In this circuit, the rectifier apparatus 4 and the circuits of tubes 8 and II are identical with those described in connection with Figure 1. However, from the cathode of the grid glow tube H the circuit is taken to brushes 24 and 25 carried on a different design of kicker. Brush 26 is connected to resistance-capacity circuit 21, 28 and a relay tube 29 as previously, and brush 30 is connected to a duplicate resistance-capacity circuit 3 I, 32 and a tube 33. The output of tubes 29 and 33 are shown connected to a push-pull winding of a polar relay 34. In this case, relay 34 is shown to be of the polar type with a neutral tongue 35 instead of the straight line relay shown in Figure 1. Polar relay 34 may be used to actuate any sort of correction mechanism, be it a small motor as shown in Figure 1, damping coils on a tuning fork, or other well known apparatus for applying correction to a controlled rotating mechanism. The preferred method of controlling the constant speed motor is to utilize a small D. C.

motor 31 in the manner shown in the box 36, which permits rotation in either direction depending upon the contact to which the tongue 35 of polar relay 34 is connected. The D. C. motor circuit 31 shows the motor field 38 in series with current limiting resistor 39 connected between plus 240 volts and minus 240 volts. The armature is connected to neutral on one side and to the tongue 35 of the relay 34 on the other side, thus enabling a reversal in the direction of the current through the armature with a resultant reversal of the direction of rotation as the relay tongue contacts with one or the other of the stationary relay contacts.

With this arrangement the control motor may be run at as nearly true synchronous speed as possible and the residual asynchronism in either direction may be corrected by rotating the field casting in the necessary direction. This is accomplished by means of the two sets of brushes 24, 30 and 25, 26. When the system is in absolute proper phase, short circuiting bars 40 of the kicker commutator are located midway between.

these two sets of brushes upon the occurrence of the striking pulse in transformer 9. If the con-' trol motor runs a little slow then brushes 25, 26 will be shorted by the bar 40 when the pulse is received and the grid glow tube II will pass a partial charge to capacity 28. If the motor remains slightly slow for a sufficient length of time, successive partial charges will finally accumulate on condenser 28 and permit the tube to attract the relay tongue 35 to the right, thus actuating the correction motor 31 and rotating the field casting in the same direction as the rotation of the armature. This will cause the armature to rotate slightly faster relative to the base-and, therefore, return the kicker commutator to proper phase. If the motor runs slightly fast, brushes 24 and 30 will be shorted when the pulse strikes the grid glow tube H and thus cause a partial charge to be passed to the left hand capacity 32. Successive pulses will finally charge this capacity to such a point as to permit the actuation of its corresponding tube 33, in turn, causing the relay tongue 35 to be pulled into engagement with the left hand contact. This will actuate the correction motor in an opposite direction to the rotation of the armature and will, therefore, again bring the kicker commutator. into proper phase relationship with the incoming signals.

Another advantage of the present invention is that the amount of hunt of the phase is limited to certain very narrow limits determined by the placement of the brushes. Occasional bad instances of fortuitous distortion may cause it to tend to overcorrect, but such tendency is prevented by the provision of a definite reverse cor- 'rection if the original correction is carried too far. Further, any permanent or quasi-permanent change in bias of the incoming signal will immediately be picked up by this arrangement and the phase of the receiving kicker will be brought into step with the new bias prevailing on the signal.

Since the only relay used in the present invention is a quick acting device in the output circuit, afurther advantage of the present arrangementresides in its quickness of operation, a characteristic due to the almost total absence of mechanical relays.

Although the presentinvention has been described with special regard to radio and carrier current communication circuits which require, reetifiers, it will be understood that the'invention is not limited thereto, since it may just as readily be applied to direct current telegraph circuits employing landlines or submarine cables by merely eliminating the rectifier and causing the incoming signals to affect resistance 1 directly or through the medium of any of the recognized terminal circuits used in the telegraph art. If desired, the primary of transformer in may be placed in series with the input circuit of resistance 1 instead of in the position shown in the drawings. Also, condensers may be used in place of transformer 9 to produce pulses on the grid of glow tube l I. Nor is the invention limited to the kickers described since other mechanical constructions may readily be used in lieu thereof It should be understood that the two types of kickers or cam arrangements shown in the drawings are interchangeable one for the other, either one being capable of use in any of the circuits shown. One particular construction which has worked out very well in practice for r,

the arrangement of Fig. 2 comprises two ordinary fractional H. P., D. C. motor commutators placed end to end on a common shaft, two commutator bars which are diametrically opposite each other being connected by jumper wires to the similarly placed bars on the other. commutator. Prefer.- ably, commutators should be chosen which have a large number of relatively narrow bars. For example, commutators having a diameter of 2 with bars of about phase width should function well. The advantage of using such a type of kicker commutator is that the construction throughout the entire periphery is the same and it ought, therefore, to wear evenly. Other forms of stroboscopic arrangements may be used for observations of synchronism and of corrector action.

Of course, the output of the relays in Figures 1 and 2 may be used to actuate other forms or types of circuits for applying a correction to the controlled motor, although the method hereinabove described is preferred since it does not require the application of correction to the source of constant speed, be it tuning fork, piezo-electric crystalor other apparatus, inasmuch as it has been found that the most accurate and most stable operation of such sources is attained when they are permitted to run without extraordinary adjustment or control.

It will be evident that this invention is not limited to the precise arrangement of parts shown, since various modifications may be made without departing from the spirit and scope thereof.

I claim:

1. In a communication system wherein communication is efl'ected by the transmission oi. signal impulses from a transmitting station to a receiving station, each or said stations having rotating machinery, the method or maintaining synchronism between the rotating mechanisms at both said stations which includes receiving the transmitted impulse, generating from the steep slopes of each impulse two pulses of diii'erent polarity, utilizing only one of said generated pulses characteristic of a particular polarity to create a positive potential charge and accumulating the successive positive potential charges to control the speed of the rotating mechanism at the receiving station.

2. A communication system having, in combination, a transmitter for sending intelligence bearing signal impulses, a remote receiver for receiving said impulses and having rotating mechanism thereat, means at said receiver for translat-ing each of said signal impulses into two pulses of diii'erent polarity, a glow discharge tube in circuit with said last means and responsive to one of said pulses of a predetermined polarity, an output circuit for said glow tube comprising a condenser of relatively large capacity and a vacuum tube relay in circuit with said condenser and responsive to a predetermined accumulative charge on said condenser resulting from a plurality of strikings of said glow discharge tube for controlling said rotating mechanism.

3. A communication system having, in combination, a transmitter for sending intelligence bearing signal impulses, a remote receiver for receiving-said impulses and having rotating mechanism thereat, means including a coupling tube at said receiver for translating each of said signal impulses into two pulses of different polarity, a glow discharge tube in circuit with said coupling tube and responsive to one of said pulses of a predetermined polarity, an output circuit for said glow tube comprising a condenser of comparatively large capacity and a vacuum tube relay in circuit with said condenser and responsive to a predetermined accumulative charge on said condens- Cl resulting from a plurality of strikings of said glow discharge tube for controlling said rotating mechanism.

4. A communication system having, in combination, a transmitter for sending intelligence bearing signal impulses, a remote receiver for receiving said impulses and having rotating mechanism thereat, means at said receiver for translating each of said signal impulses into two pulses of diiferent polarity, a glow discharge tube in circuit with said last means and responsive to one of said pulses of predetermined polarity, an output circuit for said glow tube comprising a conenscr of a relatively large capacity and a high resistance in parallel with said condenser, and a vacuum tube relayhaving an input circuit connected to said condenser and responsive to a pre- (181C: mined accumulative charge thereon resultin; from a plurality of strikings of said glow discharge tube for controlling said rotating mechan :m.

A communication system having, in combinae-ion, a transmitter for sending intelligence bearing signal impulses, a remote receiver for receivin said impulses and having rotating mechanism thereat, means at said receiver for translating each of signal impulses into two pulses of different polarity, a glow discharge tube in circuit with said last means and responsive to one of said pulses of a predetermined polarity, an output circuit for said glow tube, and a condenser, circuit interrupting means between said condenser and said glow tube for controlling the amount 01' charge to be deposited on said condenser, said glow tube being responsive only upon the occurrence of said one pulse and the simultaneous closure of the circuit by said interrupting means, a vacuum tube relay in circuit with said condenser and responsive to a predetermined accumulative charge thereon for controlling said rotating mechanisrn, said circuit interrupting means being under the control of said rotating mechanism.

6. A communication system having, in combination, a transmitter for sending intelligence bearing signal impulses, a remote receiver for receiving said impulses, means at said receiver for obtaining from each of said signal impulses a pulse or a desired polarity, a glow discharge tube in circuit with said last means and responsive to said pulse, an output circuit for said glow tube comprising a condenser of relatively large capacity and a 'high resistance in parallel with said condenser, circuit interrupting means between said condenser and said glow tube for controlling the amount of charge to be deposited on said condenser, and a vacuum tube relay in circuit with said condenser and responsive to a predetermined accumulative charge thereon resulting from a plurality of strikings of said glow discharge tube for controlling said circuit interrupting means.

7. A telegraph communication system comprising a transmitting station and a receiving station, means at said receiving station including a transformer for obtaining a synchronizing pulse from the intelligence bearing signals received from said transmitting station, a glow discharge tube whose input circuit is serially connected with the secondary winding of said transformer, an output circuit for said glow tube comprising a capacity and a resistance connected together, said condenser being arranged to charge up when current flows in said output circuit, circuit interrupting means between said condenser and said glow tube, said interrupting means comprising a rotating disc having electrically conductive contacting members spaced apart on the surface thereof and arranged to make and break the circuit between said condenser and glow tube as said disc rotates, said glow discharge tube being arranged to strike upon receipt of said synchronizing pulse only when said contacting members close said output circuit between said tube and said condenser, and a vacuum tube relay in circuit with said condenser and responsive to a predetermined acmumulative charge thereon resulting from a plurality of strikings of said glow tube for controlling said rotating disc in synchronism with the incoming signals.

8. A system as defined in claim 7, characterized in this, that said contact members on the disc are pins which are located on the periphery thereof.

9. A telegraph communication system comprising a transmitting station arranged to transmit intelligence bearing signal impulses, said signal impulses comprising high frequency oscillations, and a receiving station, a rectifier at said receiving station for translating the received high frequency signal impulses into direct current impulses whose envelope is in accordance with the received signal impulses, means including a transformer at said receiving station for obtaining a synchronizing pulse of a predetermined polarity from the envelopes of said direct current impulses, a glow tube whose input circuit is serially connected with the secondary winding of said transformer, an output circuit for said glow tube comprising a condenser and a resistance connected together, said glow tube functioning to partially charge up said condenser each time current flows in the output circuit thereof, circuit interrupting means between said condenser and said glow tube, said interrupting means comprising a rotating device having electrically conductive contacting members spaced apart on the surface thereof and arranged to make and break the circuit between said condenser and glow tube as said device rotates, said glow discharge tube being arranged to strike upon receipt of said synchronizing pulse and the simultaneous closure of the circuit by said interrupting means, and a vacuum tube relay in circuit with said condenser and responsive to an accumulative charge on said condenser for controlling said rotating device in synchronism with the incoming signals.

10. A telegraph communication system comprising a transmitting station arranged to trans mit message signal impulses, a receiving station, a vacuum tube having input and output circuits at said receiving station, a resistance connected to the input circuit of said vacuum tube, said resistance being arranged so that current passes therethrough which has a time of occurrence in accordance with the receipt by said receiving station of said message signal impulses, said vacuum tube functioning to amplify said current variations in said resistance, a reactance in the output circuit of said tube responsive to the flow of current therein for generating pulses of a predetermined polarity which have a time 'of occurrence in accordance with said incoming message signal impulses, a glow discharge tube coupled to said reactance, an output circuit for said glow discharge tube comprising a condenser -and a resistance connected in parallel, a circuit interrupter located between the condenser and said glow tube, said glow tube being arranged to strike only upon the generation of said pulses and the simultaneous closure of the circuit by said interrupter, and to place a charge upon said condenser,

and control means responsive to a predetermined charge upon said condenser for controlling the exact time of interruption of said circuit interrupter.

11. A telegraph communication system comprising a transmitting station arranged to transmit message signal impulses, a receiving station, a vacuum tube having input and output circuits at said receiving station, a resistance connected to the input circuit of said vacuum tube, said resistance being arranged so that current passes therethrough which has a time of occurrence in accordance with the receipt by said receiving station of said message signal impulses, said vacuum tube functioning to amplify said current variations in said resistance, a reactance in the output circuit of said tube responsive to the flow of current therein for generating pulses of a predetermined polarity which have a time of occurrence in accordance with said incoming message signal impulses, a glow discharge tube coupled to said reactance, an output circuit for said glow discharge tube comprising a condenser and a resistance connected in parallel, said glow discharge tube being arranged to place a charge upon said condenser upon the striking of the glow in said tube, a circuit interrupter located between the condenser and said glow tube comprising a rotating device having electrical conductive contacting members spaced apart on the surface thereof and arranged to make and break the circuit between said condenser and glow tube as said device rotates, said glow discharge tube being arranged to strike upon the generation of said pulses and the simultaneous closure of the circuit by said interrupter, a relay in circuit with said condenser and responsive to a predetermined accumulative charge on said condenser for controlling said rotating device in synchronism with the incoming message signal impulses.

12. A communication system having, incombination, a transmitter for sending intelligence bearing signal impulses, a remote receiver for receiving said impulses and having rotating mechanism thereat, means at said receiver for translating said signal impulses into synchronizing pulses, a glow discharge tube in circuit with said last means and responsive to said synchronizing pulses for causing a glow to strike, an output circuit for said glow tube including a first condenser connected in parallel with a resistance and a second condenser connected in parallel with another resistance, said glow tube when functioning being arranged to place a charge upon said condensers when connected thereto, a circuit interrupter located between said condensers and said glow tube comprising individual electrically conductive contacting members connected to each of said condensers, and a metallic bridging member for electrically connecting respectively said condensers with said glow tube, the active,con-

nection between either one of said condensers 

